We are using combined electron probe X-ray microanalyzer and electron microscope techniques to elucidate the nature of calcium sequestering pools in cells, and the nature of calcium deposits in newly forming bone. We are also using these techniques to discover the pathway followed by calcium as it moves through cells of two calcium transporting epithelia, the chick chorioallantoic membrane, and small intestine. Ancillary experiments to devise and evaluate methods for preparing cells and tissue for electron probe analysis are also being carried out.